1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a remote access (RA), and more particularly, to a remote access between a remote access client (RAC) and a remote access server (RAS) in environments in which various network address translation (NAT) devices are applied.
2. Description of the Related Art
FIG. 1 is a diagram showing cases of network address translation (NAT) applied in a Universal Plug and Play (UPnP) remote access process.
Referring to FIG. 1, various scenarios are shown according to the position of an NAT device. As shown in Cases 1 through 4, the NAT device may be on a home gateway or in an Internet Service Provider (ISP) network. AN NAT device positioned in front of a Remote Access Client (RAC) indicates an NAT device that is on a gateway in a home network to which the RAC belongs, or an NAT device that is in an ISP network.
In Case 1, no NAT device is present between a home gateway and a public network, and only one NAT device is positioned on the home gateway between an RAC and a public network. Here, the home gateway is limited to supporting an Internet Gateway Device (UPnP IGD).
In Cases 2 through 4, an NAT device is present between a RAS, that is, a home RAS, and a public network. Cases 2 through 4 are classified according to whether an NAT device is present in front of an RAC, and if an NAT is present in front of an RAC, the cases may be classified again according to the type of the NAT device. In Case 2, no NAT device is present, and in Cases 3 and 4, an NAT device is present. The NAT device of Case 3 is a Full Cone NAT, and the NAT device of Case 4 is a non-full cone NAT.
FIG. 2 is a block diagram illustrating a configuration of a related art UPnP Remote Access Architecture v1.0.
The Related Art UPnP Remote Access Architecture v1.0 operates as follows.
First, a Management Console (MC) module 240 receives an external IP address from an IGD, and calls an Inbound Connection Configuration (ICC) service interface 222 of an RAS 220 to set addresses of a Simple Traversal of User Datagram Protocol through NAT (STUN) server and a Dynamic Domain Name System (DDNS) server. Here, in addition to setting the addresses of the STUN and DDNS servers, the ICC service interface 222 can deliver information collected by a STUN client to the MC module 240. The information collected by a STUN client may be, for example, whether an RAS is with an IGD or not.                When an RAC 210 and the RAS 220 are in the same network, the MC module 240 calls Remote Access Transport Agent (RATA) Configuration services 211 and 224 of the RAS 220 and the RAC 210 to set a profile, which is a parameter for an RA transport channel.        
After the RAC 210 is separated from the network, the RAC 210 establishes a Remote Access Transport (RAT) channel connection in the external network based on the above set RATA Configuration information.
Remote Access Discovery Agents (RADA) 212 and 221 of the RAC 210 and the RAS 220 synchronize network images via the generated RAT channel. Here, the RAS 220 may set a filter of a device list of a local network that is exhibited to the outside via an RADA Configuration service 223. The RADA may synchronize tree-shaped network images with respect to an UPnP device list of local and remote networks. That is, when a device is added to a local network, an AddRemoteDevice interface of a remote network is called to add a new device to a node of a network image.
Finally, the RAC 210 discovers a service of the RAS 220 from the synchronized network image, and the RAC 210 may request the discovered service by itself via a RAT channel. Here, the RAS 220 functions as a router, and the home device 230 actually responds to the request of the RAC 210.
The above-described related art UPnP Remote Access Architecture v1.0 can support only Case 1 of FIG. 1. That is, the related art UPnP Remote Access Architecture v1.0 can support only Case 1 of FIG. 1 with no regard to whether an NAT device is present in front of an RAC or not, or to the type of the NAT device, as long as a gateway is directly connected to a public network and an RAS is present in a separate device in the home or on a gateway. However, if an NAT device is present in front of an RAS as in Cases 2 through 4, an RAC cannot connect to an RAS properly.